Volcanism and massive sulfide formation at a sedimented spreading center, Escanaba Trough, Gorda Ridge, northeast Pacific Ocean

Seismic‐reflection profiles over the sediment‐filled Escanaba Trough at the southern Gorda Ridge reveal a series of volcanic centers that pierce the sediment. The volcanic edifices are 3 to 6 km in diameter and are spaced at 15 to 20 km intervals along the axis of the trough. The volcanic intrusions have uplifted the sediment as much as 100 m, and in places fresh basaltic flows are exposed at the sea floor. Unoxidized pyrrhotite‐rich massive‐sulfide samples were obtained from the flanks of one of these volcanic centers. The composition and form of the sulfide samples suggest significant interaction between hydrothermal fluids and sediment at depth, and deposition of sulfide within the sediment pile.